Many configurations of intermingling jets are known. Generally such jets have a body through which a yarn passage extends, with one or more fluid inlets communicating with the yarn passage in a transverse direction so as to direct a jet or jets of the fluid laterally of the yarn as it passes through the yarn passage. Generally also, for intermingling purposes, the cross section of the yarn passage is symmetrical about a longitudinal axis and the axis or axes of the fluid inlet(s) intersect(s) the axis of the yarn passage so that there is no or little twisting effect on the yarn. The transverse flow of fluid causes the filaments of the running yarn to whirl about in the yarn passage and become intermingled. Such treatment jets intermingle multifilament yarns with differing degrees of success. One of the major problems of such jets is that the filaments whirl about in an uncontrolled manner so that the degree of intermingling varies along the length of the yarn, creating dye shade and feel variations in a fabric knitted or woven from the resulting yarn.